Implantable medical devices containing a reservoir which requires filling, periodic refilling or sampling are well known in medicine. Such devices or fill ports usually contain a needle penetrable, fluid impermeable septum forming at least a portion of the housing through which access to the interior of the housing, which defines a reservoir, may be gained by insertion of a hypodermic needle. In practice, the location of the fill port under the skin is first determined by extracorporeal means such as digital palpation or magnetic detection, then the hypodermic needle is driven through the skin in such a way as to puncture the septum. After the needle penetrates the septum it passes on through the reservoir until the tip comes to rest against a needle guard which provides a barrier to further progress of the needle. When the physician encounters the resistance of the needle guard and is confident that the needle tip is in the reservoir, the reservoir is filled by means of a syringe. When filling is complete, the needle is withdrawn.
While puncture of the septum usually causes minimal damage to the needle tip, contact with the needle guard can cause burring. The burring can be particularly severe if the physician taps the needle against the guard to verify correct positioning of the needle within the reservoir. Such a burred needle when withdrawn through the septum may cut or tear the elastomeric material thus reducing its tendency to self seal.
It is the object of the invention to provide an improved fill port for injection of fluids into an implanted reservoir, the improvement being positive and objective means for ascertaining correct positioning of the needle tip within the reservoir by induction of a characteristic externally mechanical vibration detectable in response to the mechanical exertion of pressure by the needle upon a flexible member situated within the reservoir. It is a further object of this invention to prevent or minimize burring of a needle used to fill an implantable injection reservoir.